Locate ducts inside the home’s conditioned space and include an efficient hot water distribution system
The Department of Energy would like builders to up their game. Though the energy savings achieved by the DOE’s Energy Star Homes program (said to be 20%) is worth celebrating, it’s possible these days to build homes that are even more energy efficient than that. It’s even possible while also delivering other key benefits: improved comfort, reduced water use, the best possible indoor air quality, and the ability to seamlessly integrate a photovoltaic (PV) system. The DOE thinks it’s time for more new homes to take that step.
Enter the Zero Energy Ready Home program. Launched in 2013 as an outgrowth of the DOE’s Builder Challenge program (which saw 14,000 homes certified), this new home certification program requires several steps above Energy Star. According to Jamie Lyons of Newport Partners, a management firm that helps the DOE administer the program, the number of ZERH certified homes has doubled from 2016 to 2018. As of late 2018 there were several thousand certified homes across the country, with approximately 10,000 in the pipeline to be certified.
A new bar for “high performance”
Our company, Deltec Building Company, operates in Asheville, North Carolina (Climate Zone 4A) and surrounding communities. Asheville is a fast-growing area due to the attractive climate and our vibrant arts and beer culture, with a booming construction market and a healthy market for green building in particular. Yet despite the local popularity of green building, no one in Asheville had built a Zero Energy Ready Home until recently.
Since our homes’ HERS scores were already right within the target range (45 to 55, pre-solar), we were ready to try it out. Our energy rater, Dr. Amy Musser of Vandemusser Design, is always up for a new challenge. I just needed to get a willing client on board, and I did so at last when John and Barry, a couple retiring to the area from their longtime home of Chicago, agreed to let their home be our testing ground.
A lot like Energy Star, with substantial add-ons
The insulation and comfort system requirements for Zero Energy Ready Home are a bit beefed up from Energy Star, but in our case, we were already doing most of those. The biggest design difference is that ZERH requires all ductwork to be 100% inside the conditioned space, whereas Energy Star merely rewards it. This makes sense, as moving ductwork inside the conditioned space offers notable energy efficiency gains; one study found it can save between 8% and 15% on air conditioned costs.
As designed, John and Barry’s home has 1,762 square feet on a slab foundation, incorporating a “split mono-slope” roof design with vaulted trusses. We typically build a conditioned attic space with a flat ceiling over a central core of hallways and bathrooms, using spray foam insulation at the roof line and exterior attic walls. We typically house a single ducted minisplit in this space, with ductwork adequate to serve the bedrooms and bathrooms that are all clustered on the back half of the house. We then serve the other half of the house — the open kitchen, living room, and dining room — with a single ductless minisplit.This two-zone system is our attempt at striking a compromise between right-sizing the unit’s capacity to the house heating and cooling load and the need to distribute the conditioned air effectively throughout the house.
In our area we have seen many contractors who are using minisplits who put one ductless unit in every bedroom, even in very well insulated homes — a design we think is overkill from a capacity and equipment cost standpoint.
The reduced hot water use requirement was the kicker*
There is a little requirement, buried within the ZERH program documents, calling for efficient hot water distribution. The ZERH checklist, V4, states: “To minimize water wasted while waiting for hot water, the hot water distribution system shall store no more than 0.5 gallons of water in any piping/manifold between the hot water source and any hot water fixture.” This requirement must be measured by the rater.
Since most homeowners flush this cooled water down the drain while they wait for the heated water to arrive, this requirement can save a considerable amount of water. Yet a water heater would have to be located close enough to all the faucets to succeed at storing this little water in the piping between them. Having to think about this might be completely new to a builder who has only built for Energy Star, and indeed, is unusual as an absolute requirement for a green building program, rather than an option for additional points.
A quick glance at John and Barry’s floorplan had me convinced at first that this project was not going to succeed at this, even if we used a manifold instead of a trunk and branch plumbing design, as the water heater was on the far side of the house from the bathrooms. Yet we had specified a heat-pump water heater for its superior energy performance over a typical electric tank water heater, a technology that John and Barry agreed to despite the operating noise and the cold air, only if they could keep this water heater away from the main living spaces. Since the home was on a slab foundation, moving the water heater under the house to be centrally located underneath the bathrooms wasn’t an option.
I hated to give up the heat-pump water heater, so I spoke to the friendly folks at the DOE about this challenge. They pointed out that ZERH does allow the use of a hot water circulation system to meet this requirement, so long as that system has the right kind of controls. In a typical hot water circulation system, an extra hot water return line makes a loop between the furthest fixtures and the water heater, while a pump is set up to circulate hot water throughout this loop. When hot water is called for, the heated water only has to travel the distance from the loop to the faucet, not the entire distance from the water heater to the faucet, reducing the amount of water that is wasted down the drain while waiting for the hot water to arrive. Long wait times for hot water is a complaint I’ve heard from homeowners before (this issue is probably made even more noticeable by lower flow fixtures). John and Barry had even asked me once, in an offhanded sort of way, if there were only a way to avoid wasting so much water.The thing is, for a Zero Energy Ready Home, this pump must be controlled by either a manual button, an adaptive control system, or an occupancy sensor that turns the pump on when it senses someone near the faucet. According to the folks at the DOE, and backed up by conversations I’ve had with our rater, many of the common methods of controlling a hot water circulation pump (such as timers or temperature sensors, or even just leaving the pump on 24/7) end up wasting considerably energy, as the system ends up operating when hot water is not actually called for. Unfortunately all of the circulation pumps that our plumber or their plumbing supply house were familiar with used timers.
Luckily the DOE has some suggestions for recirculating pumps with manual controls. After researching several options, I settled on the D’Mand Kontrol system with user activated buttons.
The system even includes LED switches that light up when the pump is activated, to alleviate the problem of one person hitting the button in one location and another inadvertently turning the pump back off by hitting it somewhere else.
It took some research to find a plumbing supplier who carried the D’mand Kontrol system, and some convincing to get our plumber comfortable with installing it. (“Yes, I specifically need this one, because it has a manual control. No, I can’t accept this alternative that uses a timer.”) There was some coordination between the plumber who would install the pump and the electrician who would install the low-voltage control wiring for the buttons. But in the end, we did get it working, and had a new selling point to offer any customer, not just those interested in a Zero Energy Ready Home: no more water wasted waiting for hot water to arrive.(*As of 5/8/2019, the DOE released a new revision on the program that has additional options for qualifying for the efficient hot water requirement that were not in effect when we completed the program. However, we think that the hot water re-circulation pump with demand control is such a good idea for situations where compact plumbing is not feasible that we still wanted to share our experience with it.)
A new focus on interior finish selections
ZERH Certification requires that the homeowner also earn Indoor Air Plus Certification, another program available from the EPA with specific requirements for indoor air quality. Many of these requirements also overlap with Energy Star, such as right-sizing your HVAC system with Manual J, installing a fresh air ventilation system, and incorporating key water management details into the building envelope and site grading.
Some requirements were new to us, and required that each interior finish selection be carefully vetted. Any composite wood product (including any cabinetry, sheathing, trim material, LVL, or engineered wood flooring that had a composite wood component), any interior paint or stain, and any carpet and even the carpet pad, had to comply with a relevant indoor air quality standard. While some of these standards were easy to identify (for example, the carpet product the homeowners had already selected had the required CRI green label clearly documented on the spec sheet, and our paint supplier was already using the Sherwin Williams Pro-Mar 200 Zero-VOC line), others required considerable research to uncover.
The interior doors proved the most interesting challenge, as the doors we typically order come from a small regional manufacturer rather than a from national supply house. We uncovered during the vetting process that those doors were in turn assembled from materials purchased from various other manufacturers. Multiple phone calls to various management levels to the manufacturer of each component used by that door supply company, were needed to ensure that the doors were in fact CARB phase II complaint. Even then, it took a special order to ensure that doors arrived on site carrying the actual CARB II sticker so we could prove it to our rater.
“Ask, verify, and then verify again” is a good manta for this kind of product specification research. We were pleased to be able to work with our normal supply companies for our interior products and not disrupt our typical ordering process, mostly because I was willing to put in the research and did so well before it was time to order. Some builders may just want to be sure to order key components from national suppliers who often have better documentation on the various VOC certifications their products hold.
“Zero Energy Ready Home” is not my favorite program name, I admit. I am skeptical that the concept of “zero energy” would makes sense to most customers and can even sound misleading. (Is it zero site energy? Zero source energy? How is it reallyzero energy in a typical net-metered situation? What do you mean my home is readyfor zero energy but isn’t necessarily zero energy?) I do get it — the concept of being “ready for zero” is about a home that puts efficiency first, so that adding solar is easy and simple.
In our case, solar was already part of the project. Our area has a decent net-metering program, and local rebates for solar offered through Duke Power that the homeowner wanted to take advantage of. Without solar, a home participating in ZERH has to complete a solar-ready checklist which include provisions for planning for future solar.
Benefits and considerations
In the end, the homeowners got a highly efficient home, with tested systems, better air quality, and reduced hot water wait times. We were fortunate that we were able to do so without compromising on the specific technologies (like the heat-pump water heater) or the specific selections (like those cabinets they really had to have) that the clients had had made. Meanwhile, we gained a few new tricks and practices to employ.
The world of voluntary green building certification programs is already a crowded one, and the sheer number of programs to choose from can be confusing for a homeowner or builder to navigate. But having gone through it now, I have to say it that the ZERH program might now be my favorite program. Unlike some of the more complex programs, like LEED or any other points-based system, it’s all-encompassing. Everything is required, nothing is optional — yet the program is simple enough that it focuses on only the best, most universal practices in building science, without getting distracted by other green building practices that are nice to have but may not fit with every job. It builds on programs and concepts that are already out there — like the Energy Star and Indoor Air Programs that are subsumed within it — but takes things further.
I think it’s a solid choice, not just for a “pretty good house”, but maybe even a darn good one.